The present invention relates to an inkjet head for an inkjet printing apparatus.
Recently, inkjet printing apparatuses are widely used. An inkjet head (i.e., a printing head) employed in an inkjet printing apparatus is configured such that ink is supplied from an ink tank into manifolds and distributed to a plurality of pressure chambers defined in the inkjet head. By selectively applying pressure to the pressure chambers, ink is selectively ejected through the nozzles, which are defined corresponding to the pressure chambers, respectively. For selectively applying pressure to respective pressure chambers, an actuator unit composed of laminated sheets of piezoelectric ceramic is widely used.
An example of such an inkjet head is disclosed in U.S. Pat. No. 5,402,159, teachings of which are incorporated herein by reference. The above-described patent discloses an inkjet head which includes an actuator unit having ceramic layers which are consecutive laminated planes extending over a plurality of pressure chambers. In the inkjet head of the above-mentioned patent, the piezoelectric ceramic layers of the actuator unit generally include active layers and inactive layers. The active layers are located at the pressure chamber side and sandwiched between a common electrode kept at a ground potential and driving electrodes (individual electrodes) respectively located at places corresponding to the pressure chambers. One inactive layer is located on a pressure chamber side and another inactive layer is located on a side opposite to the pressure chambers. By selectively controlling the potential of the driving electrodes to be different from that of the common electrodes, the active layers expand/contract in the stacked direction of the layers in accordance with a piezoelectric longitudinal effect. With this expansion/contraction of the active layers, the volume within the corresponding pressure chambers varies, thereby ink being selectively ejected from the pressure chambers. The inactive layers deform very little and serve to support the active layers from above so that the active layers effectively expand/contract in the stacked direction of the layers.
Recently, there is a great demand for highly integrated pressure chambers. However, the inkjet head of the type as described in the above-mentioned patent is insufficient to meet such a demand.